A Single-Atom Iridium Heterogeneous Catalyst in Oxygen Reduction Reaction

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Single-atom catalysts (SACs) combine benefits of homogeneous and heterogeneous catalysts for improved efficiency.
• High-performance SACs and understanding their mechanisms are crucial for ORR catalysis.
• Existing catalysts face limitations in activity, durability, and cost.

Purpose of the Study:

• To develop a high-performance iridium single-atom catalyst (Ir-SAC) for oxygen reduction reaction (ORR).
• To mimic homogeneous iridium porphyrins using an Ir-SAC structure.
• To elucidate the catalytic mechanisms behind the enhanced ORR activity.

Main Methods:

• Synthesis of an Ir-N-C single-atom catalyst.
• Electrochemical testing for ORR activity and durability.
• Atomic structural characterization (e.g., EXAFS, XANES).
• Density functional theory (DFT) calculations.

Main Results:

• The developed Ir-SAC demonstrated significantly higher ORR activity than iridium nanoparticles and commercial Pt/C.
• Achieved a record turnover frequency (TOF) of 24.3 e⁻ site⁻¹ s⁻¹ at 0.85 V.
• Exhibited an impressive mass activity of 12.2 A mg⁻¹ Ir.
• DFT calculations confirmed moderate adsorption energy of intermediates on mononuclear Ir sites.

Conclusions:

• The Ir-SAC offers a promising alternative for efficient and durable ORR catalysis.
• The unique mononuclear iridium coordinated with nitrogen sites is key to its high performance.
• This work provides fundamental insights into SACs for ORR and opens avenues for future catalyst design.